
Murderers and other people prone to violence have distinct brain patterns that can be scanned and that might be changed with drugs and other therapies, researchers said. Most people's brain can rein in overreaction to emotions such as fear or anger. But in pathologically violent people, this control system gets short-circuited. Several studies have shown this rewiring can be seen in images such as PET(positron emission tomography) scans. Impulsive,affective aggression may be the product of a failure of emotion regulation, University of Wisconsin-Madison psychologist Richard Davidson and colleagues wrote in their report, published in journal science.
They said normal people can control their emotions,and can respond to cues from other people, such facial expressions of fear. We suggest that individuals predisposed to aggression and violence have an abnormality in the central circuitry responsible for these adaptive behavioral strategies, they wrote.
Davidson and his team reviewed studies, including some of their own, involving 500 violent people with aggressive personality disorder,childhood brain injuries and convicted murderers. They compared their brain function to nonviolent people. 
They found dysfunction in the same brain regions in 41 murderers, in a group suffering from aggressive impulsive personality disorder and in some people diagnosed with antisocial personality disorder. And they found that the same brain regions were involved again and again. The evidence we have reviewed indicates that the orbitofrontal cortex and the structures with which it is interconnected, including other prefrontal territories, the anterior cingulate cortex ,and the amygdala, constitute core elements of a circuit that underlies emotion regulation,they wrote. The orbital frontal cortex is important in h olding back impulsive outbursts, while the anterior cingulate cortex recruits other brain regions in the response to conflict.
The amydala, the almond-shaped structure linked with fear and emotion ,is also and important player. In violent people, its activity essentially ran out of control, while other brain regions could calm it down in normal people. Abnormalities in serotonin function in regions of the prefrontal cortex may be especially important, the researchers added. Serotonin is an important message-carrying hormone, known as a neurotransmitter, linked with mood and emotion. It is targeted by antidepressant drugs. Davidson said genetics and environment are probably both involved and it may be possible to rewire these faulty circuits with drugs or psychological therapy. Given what we know about brain plasticity and the fact that the brain really can change in response to experience, we have good reason to expect that these treatments may, in fact, have beneficial consequences, he said in a statement. 
Meanwhile, a second report in Science suggested that aggression is not always bad. Frans de Waal of the yerkes Regional Primate Research Center in Atlanta said sometimes conflict led to closer relationships by letting peole literally kiss and make-up. For example, chimpanzees kiss and embrace after fight, and other nonhuman primates engage in similar reconciliations,he wrote. 
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